Designing Comparator Circuits with 2 Different Thresholds

[likephysics]

I am trying to design a comparator which is required to have 2 different switching thresholds.

The comparator +ve input is connected to a signal source (triangle wave). The -ve is connected to a reference voltage.

The first threshold will be say Vth+ = 3V and Vth- = 1V
and second threshold Vth+ = 8V and Vth-= 3V

I tried changing the reference voltage. But both levels either go up or down.
I added a T network in the hysteresis feedback network. The grounded resistor in t network would be open for the first set of threshold and it would be grounded for the second set. It helps a bit. I can't figure out the math of t network.

Any other ideas?

 

[jsgruszynski]

The easiest way is to allocate 3 comparators at each threshold reference level and do the hysteresis in a digital logic finite state-machine. That eliminates the variability and complexity of feedback loops and delays.

 

[skeptic2]

Can you show us your circuit?

 

[likephysics]

Skeptic2, its similar to fig. 6 in this link, but R2 (feedback resistor) is replaced by T-network.
http://www.analog.com/library/analogDialogue/archives/34-07/comparators/